The present invention relates to a device capable of signalling the inflating condition in the tires; the device comprises an external covering capable of rotating together with a threaded body used for screwing the device on the body of a standard inflating valve, a chamber defined inside the threaded body, an element sensible to the pressure existing in the chamber, a member which can be deformed by the pressure considering the temperature and a system capable of signalling the position of the deformable member.